Grease containing diphenyl p-phenylene diamine and a phosphorus acid ester and method of making said grease



Patented Dec. 22, 1.953

UNITED STATES PATENT OFFICE GREASE CONTAINING DIPHENYL P-PHENYL- ENEDIAMINE AND A PHOSPHORUS ACID ESTER AND METHOD OF MAKING SAID GREASEJohn P. Dilworth, Fishkill, iv. Y., assignor to The Texas Company, NewYork, N. Y., a corporation of Delaware N Drawing.

herewith, discloses and claims that this compound has importantadvantages over other amines commonly employed as oxidation inhibitors,including closely analogous derivatives Application February 16, 1951,Serial No. 211,447

12 Claims. (Cl. 252-421) for this purpose are tri-alkyl, aryl and mixedalkyl-aryl esters of phosphoric and phosphorous acids boiling aboveabout400 F. As examples of such compounds may be mentioned tributylphosphate, triamyl phosphite, tricresyl phosphate,

tricresyl phosphite, trixylyl phosphate and tri-' xylyl phosphite.Tricresyl phosphate, obtained from coal tar acids, is an especiallysuitableand readily available material of this type. The phosphorus acidester serves as a ,carrier'and a distributor for the N,N' diphenylpara-phenylene diamine so that the latter can be readily incorporatedinto the grease, forming a uniform and stable composition. Furthermore,it has been found that a synergistic effect of the phosphorus acid esterand the amine is thus obtained on the thermal stability of the greasecomposition, while of para-phenylene diamine, when employed in a sodiummyristate type of ball and roller bearing grease, by impartingunexpectedly superior thermal stability to the grease when used for thelubrication of anti-friction bearings at high temperatures of the orderof 300 F.

However, difficulties have been encountered in the uniform incorporationof N,N diphenyl para-phenylene diamine into such lubricating greasecompositions because of its insolubility in the high boiling organicliquid lubricating bases which normally comprise a major portion ofsuch'compositions.

When this compound is.

incorporated into greases by the usual methods employed with insolubleor difiicultly soluble additives, such as by heating the lubricant baseto a temperature above the melting point of the additive compound or byadding the latter to the lubricant base or grease in solution in a lightorganic solvent, which is later flashed off, nonuniform lubricatinggrease compositions may be produced'having widely varyingthermalstability characteristics, and the N,N' diphenyl paraphenylenediamine shows a tendency to crystal-- lize out of the grease uponcooling.

It is accordingly a principal object of the present invention to providean improved grease composition, and a method of manufacturing suchdiphenyl para' composition, containing N,N' phenylene diamine, whereby auniform composition having superior thermal stability and 1 otheradvantages is obtained.

In accordance with the present invention, this is accomplished by addingto such lubricating grease compositions a minor amount of N,N di-'phenyl para-phenylene diamine dissolved in an oil-soluble ester of aphosphorus acid. Phos-' phorus acid esters which are particularlysuitable ,in addition known anti-wear properties of the phosphorus acidester are imparted to the grease. A suitable inhibitor compositionof myinvention comprises tricresyl phosphate containing dissolvedtherein'N,N' diphenyl para-phenylene diamine in at least a 2.521 weightratio and up to about :1 or higher depending upon the permissible amountof tricresyl phosphate which may be added to the grease, and preferablyabout a 2.721 to 4:1 weight ratio. Such a solution may be obtained bydissolving N,N' diphenyl paraphenylene diamine in tricresyl phosphatewhen the latter is heated at about 200 F. At this temperature tricresylphosphate dissolves a little over one third of its weight of N,N'diphenyl para-phenylene diamine.

A solution of N,N' diphenyl para-phenylenef diamine in an oil-solublephosphorus acid ester obtained in the above described manner, or in,

any other suitable manner, is added to lubricating grease compositionsin amounts sufi-lcient to impart the desired thermal stability,oxidation resistance and anti-wear properties to the latter.

Generally, the solution is added in an amount such that the lubricatingcomposition contains from about 0.1 per cent toabout 3 per cent, and

preferably from about 0.5 per cent to about 2i per cent by weight ofN,N' diphenyl para phenylene diamine. V v

1 Lubricating grease compositions to which the inhibitor composition ofmy invention may be added-suitably comprise in substantial proportion ahigh boiling organic oil, which may be a mine eral oil fraction obtainedfrom a parafiinic, naphthenic or mixed base crude by any of the usualrefining methods, an animal or vegetable oil such as lard oil, corn oil,castor oil, or the like, ora synthetic oil obtained by polymerization"or chemical condensation, as well as mixtures of these. The lubricatingcompositions may contain any of the usual additives in so far as noincompatibility exists between them and the additives of my invention,as well as thickening agents such as fatty acid soaps in grease formingproportions.

An especially valuable embodiment of my invention comprisesimpartingsuperior thermal stability to a sodium base 'balll'and'jrollerhearing grease prepared from a'mixture of low molecular weight fattyacids comprising at least '70 per cent, and preferably atleast 90 percent, of myristie acid and/ or the glyceridesthereof, The greasepreferably comprises from about per cent to about per cent of asoapobtained by saponifying such a fatty acid mixture with ya small excessof alkali, and a lubricating oil which may suitably be a blend of adistillate oil andea residual oil from a parafiinic stock. Greases ofthis type are-particularly useful as lubricants for ball and rollerbearings operated at high rotative. speeds and under elevatedtemperatures up to.300 F. and above.

The table below gives data obtained onsevral greases of the above typecontaining "N,N' diphenyl para-phenylene diamine as the oxidation'.inhibitor which was added both by the conventional. methods and .by themethod of my invention. Comparative .data are also included on anuninhibited grease of this type and on such solved in a mixture ofbenzene and acetone and added to a portion of the base oil at 250 F. Themixture was then heated for four hours to drive oft the solvent and theremaining composition added to the grease at the end of themanufacturing process. In the preparation of Grease #4,

the Nil 'diphenyl para-phenylene diamine was added to the grease in theform of a slurry in a part of the residual base oil at the end of themanufacturing process. In the case of Greases #5, #6 and #7, the Nildiphenyl para-phenylene diamine was dissolved in tricresyl phosphate atabout 200 F. and the resulting solution added to the grease at the endof the manufacturing process while the grease was at a temperature ofabout 200 F. The additive solutionis generally stirred into the greasefollowing dehydration and after the temperature of the gr ease hasdropped below 250 F.

TABLE Grease composition, percent:

- Na myristate Distillate oil Residual 01 Tricresyl phosphate.

Method of DPD 1 addition Tests on product;

/ Droppingpoint, .F

Unworked penetration. Worked penetration- 7 Free NaOH, percent.

Free fatty acid, percent Ngrma-Hofimann oxidation, pressure drop in 100ours.

High temperature performance test {300 F., 10,000

R. P. M.) hours to failure.

In benzene acetone at 300 F. solved in tn solvent.

1 DPD is N,N diphenyl p-phenylene diamine.

a grease inhibited with an amine oxidation inhibitor of the usual type.

' The greases were prepared by saponification of myristic acid with aslight, excess of sodium hydroxide solution in the presence of a smallamount of mineral oil and water, dehydrating theresulting soap baseandadding sufficient mineral oil to obtain the desired consistency. Themyristic acid employed had a saponification number of 245, aneutralization number of 242 and a titer of 45.7" C. The mineral oil wasa blend comprising about 14 to 19 per cent of a solvent refined and claytreatedparafiinic distillate oil having an SUS viscosity of 93 at 210 F.andthe remainder a solvent refined, clay and acidtreated paraffinicresidual oil having an SUS viscosity'of .120 at 210 F. Thesaponifioation was carried out by heating the charge consisting of myri'stic acid with about two thirds its weight ofthe distillate oil and alike amount of water to 170-190 F. and adding the sodium hydroxidesolution with stirring. After thesaponification the The Norma-Hofimannoxidation test of the foregoing table is a measure of the resistance tooxidation of lubricating greases when stored under static conditions forlong periods-oftime, as when coated in thin films on anti-frictionbearings, motor parts, etc. In this'test, five fourgram samples of thegrease are put in fiat sample dishes and placed in a stainless steelbomb sealed with a lead gasket in an atmosphere of oxygen under aninitial pressure of 110 pounds per square inch at a temperature of 210F. The pressure drop in pounds within the-bomb is then recorded atintervals of hours up to 400 hours or until a pressure drop of 55 poundsper square inch occurs.

The high temperature performance test is a test for determining theperformance characteristics of greases in anti-friction bearings atelevated temperatures and high rotative speeds. The test unit consistsessentially of a steel spindle supported on ball bearings and driven byan electric' motor connected into an electric circuit con- Y aecaectaininga low amperage fuse 0.1 ampere below that required for full loadrunning. The bearings are Norma-Hofimann ABEC No. 3 grade and, aremounted on the spindle approximately 5% inches apart. A thrust load of17.5 pounds is applied to these bearings. One of the bearings, whichserves as the test bearing, is surrounded by an electrically heatedhousing. The other bearing is outside the heated chamber and serves onlyas a guide bearing. The test consists of operating the test bearing fortwenty-four hours at 10,000 R. P. M. and 300 F., followed by a shut downand cooling period of two hours, and repeating this cycle until thelubricant fails, which is indicated by rupture of the lowamperage fusein the motor circuit. In starting up the test, three grams of the testgrease are charged to the test bearing and worked into and around theraces and balls. The test bearing is next rotated both clockwise andcounter-clockwise for one minute each at 200 R. P. M. and assembled intothe test unit. The heaters and the motor are then started and the testbearing brought up to the test temperature of 300 F. as rapidly aspossible, which requires 1.0 to 1.25 hours, while the spindle is rotatedat a speed of 10,000 R. P. M. After 24 hours of operation the heatersand motor are shut on for 2 hours, during which the temperature of thetest bearing drops to a minimum of 120130 F. The total hours ofoperation, excluding the two hour shut-down periods, to the failurepoint is recorded as the hours to failure."

As shown in the foregoing table, greases hav--- ing excellent thermalstability and other lubricating properties for high temperature ball androller bearing service are produced by adding a minor proportion of N ,Ndiphenyl para-phenylene diamine dissolved in a small amount of tricresylphosphate to sodium myristate base greases. The greases thus producedare markedly superior in these properties to greases of similarcomposition and manufacture having the inhibitor added according to theusual methods.

While the above examples serve to illustrate the results obtainable bythe method of my invention, it is not intended to limit my invention tothe manufacture of sodium myristate greases, since it is of generalapplication to greases of various soap bases where highly effectiveoxidation resistance and/or thermal stability, in addition to anti-wearqualities, are desired. Thus it may be employed for improving lithium,calcium, barium or mixed base greases for various types of service. 7

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. A lubricating grease compositioncomp-rising a lubricating oil, ametal soap of a fatty acid in grease forming proportion, a minor amountsufiicient to impart thermal stability properties to the composition ofN,N' diphenyl para-phenylene diamine added to the composition insolution in a minor amount of an oil-soluble phosphorus acid ester, thelatter serving as a carrier and a dispersing agent for the N ,N diphenylpara-phenylene diamine.

2. Claim 1 wherein the phosphorus acid ester is tricresyl phosphate.

3. Claim 1 wherein the N,N' diphenyl paraphenylene diamine comprisesbetween about 0.1- per cent and about 8 per cent of the total weight ofthe lubricating composition.

4. Claim 1 wherein the metal soap is sodium myristate.

5. Claim 1 wherein the lubricating oil is a blend residual oil of aparaflin' of a distillate and a base stock.

6. A lubricating grease consisting essentially of the followingingredients in the approximate specified proportions.

- Per cent Sodium myristate 15-25 N,N' diphenyl para-phenylene diamine0.5-5 Tricresyl phosphate 1.5-15 Lubricating oil, remainder.

7. A lubricating grease consisting essentially of the followingingredients in the approximate Lubricating oil comprising a blend of aparaffinic distillate oil and a paraffinic residual oil, remainder.

8. The method of improving the thermal stability of a lubricating greasecomposition consisting essentially of a lubricating oil and a fatty acidsoap by adding thereto a small proportion of N,N diphenyl para-phenylenediamine dissolved in tricresyl phosphate.

9. The method of manufacturing a ball and. roller bearing grease adaptedfor high temperature lubrication of anti-friction bearings, whichcomprises saponifying a fatty material containing at least '70 per centof a myristic acid with an excess of caustic soda in the presence of asmall proportion of lubricating oil ultimately present in the grease,dehydrating the resulting saponi fled material by heating to 295-320 F.,adding additional lubricating oil to the dehydrated product as thetemperature is lowered to obtain a grease of buttery consistency, andadding to the grease with stirring when the temperature has droppedbelow 250 F. a solution of N,N diphenyl para-phenylene diamine intricresyl phosphate in an amount effective to materially improve thethermal properties of the grease.

10. The method of manufacturing a ball and roller bearing grease adaptedfor high temperature lubrication of antifriction bearings, whichcomprises saponifying a fatty material containing at least per centmyristic acid with a small excess of caustic soda in the presence of asmall proportion of lubricating oil equal to about two thirds the weightof the fatty material and of a small amount of water approximately equalto the weight of the lubricating oil, then heating the saponificationmass at 295-320 F. for at least two hours to effect dehydration, thenlowering the temperature of the mass gradually to 260 F. while an amountof lubricating oil is added sufficient to bring the total lubricatingoil content of the mass to at least twice the weight of fatty materialinitially charged, then adding to the mass at a temperature below 260 F.additional lubricating oil sufficient to give a finished product havinga soap content between about 15 per cent and about 25 per cent byweight, and adding to the mass at a temperature below about 250 F. asolution of N,N' diphenyl para-phenylene di- Per cent Sodium myristate15-25 N ,N diphenyl para-phenylene diamine 0.5 5

Tricresyl phosphate 1.5-15 Lubricating oil, remainder.

said N,N diphenyl para-phenylene diamine being uniformly dispersedthrough the grease :by addition in solution in the said tricresylphosphate.

' JOHN P. .DILWORTH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,229,030 Adams Jan. 21, 1941 2,351,384 Woods June 13, 19442,369,705 Woodward et al Feb. 20, 1945 2,406,655 Bax et a1 Aug. 2'7,1946 2,406,722 Vincent Aug. 27, 1946 2,428,123 Morgan et al Sept. 30,19.47 2,542,570 Puryear Feb. 20, 1951

1. A LUBRICATING GREASE COMPOSITION COMPRISING A LUBRICATING OIL, AMETAL SOAP OF A FATTY ACID IN GREASE FORMING PROPORTION, A MINOR AMOUNTSUFFICIENT TO IMPART THERMAL STABILITY PROPERTIES TO THE COMPOSITION OFN,N'' DIPHENYL PARA-PHENYLENE DIAMINE ADDED TO THE COMPOSITION INSOLUTION IN A MINOR AMOUNT OF AN OIL-SOLUBLE PHOSPHOROUS ACID ESTER, THELATTER SERVING AS A CARRIER AND A DISPERSING AGENT FOR THE N,N''DIPHENYL PARA-PHENYLENE DIAMINE.